Arc welding systems with robot mounted welding torches have been developed to improve weld uniformity and reproduceability and to increase productivity in arc welding fabrication. Some systems have been developed using no joint or weld detection system, but instead are preprogrammed to provide a fixed sequence of motions and process actions. Such a system then merely repeats the sequence of motions and process actions for each weld. In order for such a system to operate effectively, both the welding equipment and the workpiece must be precisely positioned with reliable repetition. Any deviation in the welding equipment, the positioning of the workpiece or the path of the joint results in an inadequate weld.
Other systems have been developed to detect the joint or seam or otherwise detect or sense the weld conditions and adjust the weld parameters and torch positioning accordingly. Among these are vision systems utilizing optical detection for detecting weld and joint position and dimensional parameters.
The above identified copending application discloses a torch with a coaxial vision system which is used to obtain the weld image. In that torch an imaging lens is placed inside the gas cup so that the optical axis is coincident with the axis of the weld torch and the weld electrode. In that system an associated optical system converts the optical image of the weld pool and the weld joint to electronic video signals so that the image can be analyzed in real time and the results of the analysis used to control the welding operation. For example, the middle and edges of the weld pool and the joint are detected and used by the electronic control system to develop signals which control the weld parameters. Cross seam control is obtained by detecting the center of the weld pool relative to the weld joint. The width of the joint opening is used to control the cold wire feed and the width of the weld pool is used to control weld current.
Typically, the weld image is converted to electronic signals by means of a television camera of a type which is commercially available. One difficulty with such a system is that, although the weld torch must be capable of moving in many directions and may even rotate about its central axis, such motion causes the image in the television camera to be similarly rotated or oriented as it follows the weld joint with the result that the image of the joint may be projected onto the detector of the television camera at various angles. This variation in the orientation of the weld seam and joint greatly complicates the process of analyzing the video data for control of the welding process.
It is therefore an object and purpose of the present invention to provide an optical system which maintains the identical weld joint and seam orientation in the television camera, thereby greatly simplifying computer analysis of the video data.
Another problem with utilizing a television camera is the need to control the intensity of the light which is incident upon the detector of the camera so that this intensity is within the operating range for which the camera was designed. This is complicated by the fact that the light from the weld pool region, which is immediately adjacent the arc, has a considerably higher intensity than the light from the joint and yet a sufficiently high resolution image showing the details of both is needed.
It is therefore an object and feature of the present invention to provide an optical system which will control the intensity of the light from the weld pool region and maintain it within the operating range of the television camera and yet will permit the imaging and detection of image data from the relatively darker joint region.